1:M relationship - How do I remove & add the new ones
I have a table which has a
Unit : Unit-Teaches : INSTRUCTOR
1 : M : 1
Unit-Teaches hold the unit_key (UNit table) & instructor_key(Instructor Table)
A Unit can have one to many instructor. So the user when they update the unit can change all the instructor , add one/many or delete one/many.. My question how do I do this in a CMP and CMR? Should I be deleting all the record in the UNit-Teaches and then add again from the list I get from the user. Or how would I loop from the ones already existing and the ones I want to add or delete?
//get the collection of Instructor already associated to this unit.
Collection col = ul.getCrse_unit_instructor
Iterator it = col.iterator();
while(it.hasNext)
{
Crse_unit_instructor_teach
Long instKey = uitl.getInstr_instructor_f
//Loop through the instructor list selected by the user.
for(int i=0; i < unit.getUnitInstructorList
{
//get the instructor key
Long instructorKey = unit.getUnitInstructorList
ul.addUnitInstructorRelati
}
}
Any help would be appreciated
Unit : Unit-Teaches : INSTRUCTOR
1 : M : 1
Unit-Teaches hold the unit_key (UNit table) & instructor_key(Instructor Table)
A Unit can have one to many instructor. So the user when they update the unit can change all the instructor , add one/many or delete one/many.. My question how do I do this in a CMP and CMR? Should I be deleting all the record in the UNit-Teaches and then add again from the list I get from the user. Or how would I loop from the ones already existing and the ones I want to add or delete?
//get the collection of Instructor already associated to this unit.
Collection col = ul.getCrse_unit_instructor
Iterator it = col.iterator();
while(it.hasNext)
{
Crse_unit_instructor_teach
Long instKey = uitl.getInstr_instructor_f
//Loop through the instructor list selected by the user.
for(int i=0; i < unit.getUnitInstructorList
{
//get the instructor key
Long instructorKey = unit.getUnitInstructorList
ul.addUnitInstructorRelati
}
}
Any help would be appreciated
ASKER
I understand that but how do I loop to know which ones I need to remove and which ones are the same and which one I need to add..
I guess I need to loop through the list and add them and them loop through the list again and remove the ones I no longer want.. Is this correct?
I guess I need to loop through the list and add them and them loop through the list again and remove the ones I no longer want.. Is this correct?
>> I guess I need to loop through the list and add them and them loop through the list again and remove the ones I no longer want.. Is this correct?
How are you presenting the information to the user? How is the user input transferred into business logic?
I would present a list of all instructors, and a list of instructors associated with the unit to the user. I would keep an empty list of instructors to add and one for the ones to remove from a unit behinds the scenes, and when the user adds or removes instructors, you can keep track of it like that. After editing is done, you can find out which instructors were added/removed from a unit and update the database table accordingly.
How are you presenting the information to the user? How is the user input transferred into business logic?
I would present a list of all instructors, and a list of instructors associated with the unit to the user. I would keep an empty list of instructors to add and one for the ones to remove from a unit behinds the scenes, and when the user adds or removes instructors, you can keep track of it like that. After editing is done, you can find out which instructors were added/removed from a unit and update the database table accordingly.
ASKER
It is displayed as a multiple select list .
So by unselecting the instructor it just doesn't get passed in the String[] so I receive the list they want to add/exist.. If I also get the collection of the UNIT-Teaches this gives me
which ones are already in the database.. so then I need to loop and find out if it already exist if it does do nothing if it doesn't add it.. Then I also need to see if what is in the already existing list if it is no longer in the list the user has passed to me I need to delete it..
Does that make sense?
So by unselecting the instructor it just doesn't get passed in the String[] so I receive the list they want to add/exist.. If I also get the collection of the UNIT-Teaches this gives me
which ones are already in the database.. so then I need to loop and find out if it already exist if it does do nothing if it doesn't add it.. Then I also need to see if what is in the already existing list if it is no longer in the list the user has passed to me I need to delete it..
Does that make sense?
ASKER CERTIFIED SOLUTION
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Uniqueness is on the combination of the two keys, which means that all the key combinations should be unique, i.e. there will only ever be one record of a certain combination of unit_key and instructor_key.